482 M. C. Lea — Nature of Certain Solutions 



To explain this contrast it is necessary to remember that a 

 salt reddens litmus whenever the affinity of its acid for the 

 potash in litmus is not held in check by two affinities which 

 oppose it, that of the base for its acid and that of the litmus 

 dye for its potash. If the base is sufficiently weak, the affinity 

 of its acid for potash preponderates.* The whole question 

 therefore reduces itself to that of the strength of the base 

 with which the acid is united, and it consequently follows 

 irresistibly that even very weak alkaloids are stronger bases 

 than such metallic oxides as those of zinc, copper, cobalt, etc. 



Although this deduction seems clear it may be supported 

 by additional evidence. As bases, the alkaloids vary very 

 greatly in strength. A few which contain no oxygen are 

 bases approximating to ammonia in strength. Such are nicotia 

 and conia. Among those which contain oxygen there is much 

 difference in strength, morphia and cocleia are strong bases and 

 are known to precipitate iron, copper, cobalt and nickel salts. 

 The weaker alkaloids do not seem to have been examined in 

 this respect and one therefore was selected for examination. 



Brucia is one of the weaker alkaloids. It is precipitated 

 from its saline solutions by morphia, strychnia, etc. It forms 

 a neutral and an acid sulphate both crystallizing well. The 

 alkaloid itself is very sparingly soluble in cold water, it is 

 therefore convenient to operate with solutions raised to a 

 temperature of 50° or 60° C. The sulphates of zinc, cadmium, 

 copper, manganese, nickel and cobalt, proved to be readily 

 precipitated by brucia. The reaction is always easily obtained 

 and well marked. It is particularly so in the case of cobalt, 

 the rose red solution of which becomes quickly filled with blue 

 flocks of oxide. 



That weak bases such as the oxides of zinc, cadmium, and 

 copper should be precipitated by a weak alkaloid like brucia 

 is not surprising but the case is somewhat different with 

 stronger bases like manganous oxide and the oxides of nickel 

 and cobalt. These two last are classed by Mendeleef as 

 " fairly energetic " bases. This, however, can be understood 

 only by comparison ; no base can be considered as a strong one 

 whose neutral salts redden litmus. 



When brucia is added to solution of magnesium sulphate 

 there is no precipitation. Magnesia is a stronger base and its 

 salts are neutral to litmus not because the acids are more fully 

 saturated by it but because the potash of the litmus is unable 

 to detach the acids from the base. 



* It is of interest to observe that the reaction may be changed by the presence 

 of an additional substance although the latter may be quite neutral. Thus mer- 

 curic chloride is faintly acid to litmus, but not after the addition of potassium 

 chloride. The tendency to form a double salt changes the balance of affinities. 



